1. Field of the Invention
The present invention relates to a method for improving integrated circuits bonding firmness and, more particularly, to regular or irregular layout patterns formed under bond pads.
2. Description of the Prior Art
As the increment of integration, the multi-level interconnection must be used for the coupling of internal circuits during the fabrication of semiconductor devices because that the single metal connect is not sufficient for using. In general, many semiconductor devices utilize bond pads and bond wires to form the electrically coupling between internal and external circuits. Because the bond pads are formed on the upper metal layer of the multi-level interconnection, the upper metal layer of the multi-level interconnection are usually called as xe2x80x9cbond pad metal layerxe2x80x9d. The formation of bond pads includes photolithography and etching processes to form bond pad windows in the passivation layer, which covers the devices formed previously, and then expose the predetermined areas located in the xe2x80x9cbond pad metal layerxe2x80x9d. After the bond pad windows are formed, thin wires are bonded into the bond pad windows to couple with the predetermined areas served as bond pads.
The bond wires are tensioned and sheared during the devices are packaged, which may cause the peeling of bond wires and thus bring about the failure of the devices. There are many prior arts to solve the foregoing problem. For example, the U.S. Pat. No. 5,695,592 (Dec. 9, 1997) entitled xe2x80x9cMethod of adhesively bonding mineral particles to supportxe2x80x9d or the U.S. Pat. No. 5,700,581 (Dec. 23, 1997) entitled xe2x80x9cSolvent-free expoxy based adhesives for semiconductor chip attachmentxe2x80x9d. Another method is to modify the structure of bond pads for increasing firmness of bond wire. For example, the U.S. Pat. No. 5,686,762 (Nov. 11, 1997) titled xe2x80x9cSemiconductor device with improved bond padsxe2x80x9d. Among these methods, the U.S. Pat. No. 5,686,762 is described accompanied with the FIG. 1. At least one opening is formed in the bonding surface of bond pads and the opening(s) 22 may recesses extending partially into the bonding surface or channels that extend entirely through the bond pad. This method increases the firmness of bond wire efficiently but additional steps are needed during the forming of opening(s) 22. Such as an additional photomask of the opening(s) 22 pattern additional photolithography process removal of the photoresistor and etching processes process and so on. In FIG. 1, the object 12 is an internal circuit; the object 16 is the bond pad window; the object 18 is a passivation layer and the object 20 is an insulator layer.
The method disclosed in the present invention is easier than aforesaid methods, because additional steps or cost is not necessary for the present invention. The feature of the present invention is to make the bonding surface of metal layer under and most close to the bond pad layer (the top metal layer of multi-level interconnection) rough, which leads to improving the firmness of bond wire. The principle of roughness process is, under the predetermined regions serve as bond pads, to form a metal layer with regular or irregular layout patterns. It""s worthy to note that the roughness process is be implemented in the meanwhile of the deposition of the metal layer under the bond pad layer. In other words, it doesn""t require additional steps or cost because the photomasks of layout pattern and that of metal layer are the same one.
During the devices are packaged, the break of bond wires or the peeling of bond pads occurs frequently and thus result in the failure of the devices. In order to improve the firmness of bond wires, the present invention discloses a method, which makes the metal layer under and most close to the bond pad metal layer (the upper metal layer of multi-level interconnection) rough. The method of making rough is, under the bond pad metal, to form a metal layer with regular or irregular layout patterns to result in the undulation of upper surface. The bonding surface of later bond pads formed on the metal is affected by the undulation, and thus improves the firmness of bond wires.
The preferred embodiment of the present invention is described as follow: An internal circuit is formed on a substrate by conventional method. This internal circuit comprises several metal-oxide semiconductors (MOSs) or other semiconductor devices. An insulator layer is formed on the internal circuit and then several contact holes are formed in the insulator layer by photolithography and etching processes. Several plugs are formed in the contact holes and couple to the internal circuit. A composition layer is formed, which serves as a part of the multi-level interconnection. The composition layer is composed with at least one metal layer and at least one inter-metal dielectric layer (IMD), and each film of the composition layer is piled on top of each other. The bottom and the top of the composition layer are a metal layer and a dielectric layer, respectively. There are several vias and several via plugs in each inter-metal dielectric layer, and these via plugs serve to make the metal layers coupling to the internal circuit. It""s worthy to note that, under the specific regions serving as bond pads, the top metal layer of the composition layer has a regular or an irregular layout pattern.
The method disclosed in the present invention is applied in multi-level interconnection. If the number of metal layers of the multi-level interconnection is 3, the number of metal layers of the composition layer is 2; the inter-metal dielectric layers (IMD) of the composition layer serve as insulation and whose number is 2, as well.
A bond pad layer is formed on the composition layer. Then a passivation layer is formed on the bond pad layer. The passivation layer serves to protect the internal circuit from moisture and alkali ions. Then by photolithography and etching processes; bond pad windows are formed in the passivation layer to expose the bond pad layer. Finally, the bond wires are bonded to the bond pads.
After the aforesaid steps are finished, a test machine was used to test the firmness of the bond wires. The test result reveals that no matter whether ball shear test or wire pull test, the bond pads using present invention satisfy the industrial standard (wire pull is 5 mg and ball shear is 30 mg)